Researchers have found that patients with severe Covid-19 have significantly elevated levels of a certain type of immune cells in their blood, called myeloid-derived suppressor cells.
In the study, published in the Journal of Clinical Investigation, the team researched one type of immune cell, monocytic myeloid-derived suppressor cells, or M-MDSC, and their potential role in Covid-19.
"Our results help increase the understanding of what causes severe Covid-19 and is an important piece of the puzzle in understanding the connection between the early, innate immune system, which includes M-MDSC, and the later, adaptive immune system, which includes T cells," said researcher Anna Smed Sorensen from Karolinska Institutet.
T cells are part of the immune system and play an important part in the body's protection against viral infections such as Covid-19. M-MDSCs have been shown to increase in other inflammatory conditions, and their suppressive effect on T cell activity has been established.
The role of M-MDSC in respiratory infections, however, is largely unknown. Since low levels of T cells are a hallmark of Covid-19, it is of interest to understand the role of M-MDSCs in this disease.
The study consisted of 147 patients with mild to fatal Covid-19 who were sampled repeatedly from blood and the respiratory tract. These were then compared with patients with influenza and healthy individuals.
The results showed that patients with severe Covid-19 have significantly elevated levels of M-MDSCs in blood compared with milder cases and healthy individuals.
Covid-19 patients had fewer T cells in blood than healthy subjects, and they showed signs of impaired function.
The analysis also showed that the levels of M-MDSCs early in the course of disease seemed to reflect subsequent disease severity.
"There is also a strong clinical connection, as you could potentially use the results to find new biomarkers for severe illness," Sorensen added.
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